Structures resistant to attack

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KarelPeeters
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Structures resistant to attack

Post by KarelPeeters » June 12th, 2021, 9:58 am

Hey,

I'm new to this forum (and to "advanced" GoL), I tried to look around for similar questions but I guess I couldn't come up with the right terms.

I was wondering if there are any (non-trivial) structures that are resistant to attack from the outside. What I mean by this is a structure that stays stable around the origin no matter what the cells outside of the bounding box start out as. For example there could be a bunch of glider guns aimed at it, or even just an infinite plane of randomly initialized cells. The core requirement is that the pattern should stay stable no matter what happens outside of it. Of course the edges could temporarily change in response to "being hit" but some inner core needs to stay intact.

I'm wondering if any patterns like this exist and are known. I came up with this idea from my intuition that all complex patterns are very unstable, completely collapsing once there is a small disturbance anywhere, and it's be interesting to see if there is anything that breaks that intuition.

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dvgrn
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Re: Structures resistant to attack

Post by dvgrn » June 12th, 2021, 12:12 pm

KarelPeeters wrote:
June 12th, 2021, 9:58 am
I was wondering if there are any (non-trivial) structures that are resistant to attack from the outside. What I mean by this is a structure that stays stable around the origin no matter what the cells outside of the bounding box start out as. For example there could be a bunch of glider guns aimed at it, or even just an infinite plane of randomly initialized cells.
Yeah, these discussions do happen every few years, but they're hard to find via search. Here's probably the earliest conwaylife.com thread on the topic (though of course the question was discussed intermittently in newsletters, email groups, etc., for more than three decades before that).

Maybe you'd also be interested in the discussion of IceNine from half a decade ago. The idea there is that it's hard to absolutely rule out the possibility of active structures that reliably maintain a boundary around themselves. Nobody really thinks that IceNine actually exists in Conway's Life. An engineered version of it would have to have repair units that could respond much faster than they could realistically respond, due to speed-of-light limitations. So it would have to be a super-lucky "natural phenomenon", and collective Lifenthusiast intuition suggests that there probably isn't any such thing. On the other hand, collective Lifenthusiast intuition isn't always particularly reliable!

Another related discussion is the Clearing Pattern thread.

The most recent round of discussion of indestructible stuff, or at least probabilistically indestructible stuff (like replicators that reproduce on average faster than they get destroyed) was on the ConwayLife Lounge (Discord server) just a month or so ago. There was also Moosey's ambitious thread on the forums, from a couple of years back.

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Re: Structures resistant to attack

Post by KarelPeeters » June 16th, 2021, 4:35 pm

Hey! Sorry it took such a long time to reply!

Thanks for the interesting links! It seems like there is so much stuff to read about, the forums and wiki have a high branching factor :). It's a bit disappointing that it's probably not possible, we'll never have actual life in GoL then!

It seems like this is possible in different rulesets (eg the Starwars one, see viewtopic.php?p=130572#p130572), I'll have to do some reading/experimenting as for why that is the case.

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Re: Structures resistant to attack

Post by dvgrn » June 16th, 2021, 9:52 pm

KarelPeeters wrote:
June 16th, 2021, 4:35 pm
Hey! Sorry it took such a long time to reply!

Thanks for the interesting links! It seems like there is so much stuff to read about, the forums and wiki have a high branching factor :). It's a bit disappointing that it's probably not possible, we'll never have actual life in GoL then!

It seems like this is possible in different rulesets (eg the Starwars one, see viewtopic.php?p=130572#p130572), I'll have to do some reading/experimenting as for why that is the case.
Yup, it's easy to find/design a rule that supports invulnerable structures. The problem is that then you end up with... well... invulnerable structures. Probably all over the place.

They're great things if you happen to want them exactly where they are, but they're just plain impossible to move out of the way when you don't want them.

We can still have life forms in Life if we figure out how to put them on a computer at all... they'll just have to be set up very carefully with definite rules about the grid structure, so that you're really running whatever non-Life program you might want to run to simulate evolving organisms.

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Re: Structures resistant to attack

Post by KarelPeeters » June 17th, 2021, 5:39 am

Huh that's an interesting point, if indestructible patterns are possible you'll have them everywhere, which means you still can't really have structures that move around freely.

What do you mean with the computer thing? Of course we can compile Spore or something to a Turing machine and run that, but in the same spirit we can just do anything we want so that's not really that significant.

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Re: Structures resistant to attack

Post by dvgrn » June 17th, 2021, 7:24 am

KarelPeeters wrote:
June 17th, 2021, 5:39 am
What do you mean with the computer thing? Of course we can compile Spore or something to a Turing machine and run that, but in the same spirit we can just do anything we want so that's not really that significant.
Yeah, that's pretty much what I mean. You're really right that we "can't have life in Life", in the sense that we can't start from a random state and expect to see anything like normal evolution of life-like behavior. On a large enough grid -- required size depending somewhat on the probability of each cell being ON -- we would see some self-replication, and even some competition between self-replicators, but random ash is just too unpredictably toxic.

Maybe some replicators will have a clever enough replication method to succeed more often than they fail, for a while, and be able to build some kind of defensive perimeter that will protect them from occasional stray gliders. The big problem is a lack of potential for a replicator to have any kind of awareness of its surroundings, or any likely ability to either adapt to them or modify them.

Any replicator in an old Life universe is navigating a minefield, and it's pretty much made out of explosives. People have done a lot of hand-waving over the years about "maybe there are replicators that can clear a space around them", but there's no sign that that's really possible even in an infinite Life universe -- it's sort of like saying "maybe there are self-driving cars that can drive around at 100mph without any external sensors, carrying something highly explosive, in an environment filled with obstacles and caltrops and other highly explosive vehicles and occasional land mines".

Even saying "we'll build a billion of these self-driving cars, and pick whichever one survives longest", doesn't add much credibility. Maybe one replicator will be luckier than the others, but that doesn't mean that it has a reliable mechanism for testing its environment and safely making changes. Basically it's only going to be safe as long as it has empty space around it. The speed of light in Conway's Life is just too slow for hypothetical organisms to be able to react to their environment fast enough to keep toxic stuff from destroying them.

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Re: Structures resistant to attack

Post by hotdogPi » June 17th, 2021, 8:17 am

Other rules have quadratic replicators that replicate fast enough that copies just go around whatever is in their way. Is that any more likely?
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Re: Structures resistant to attack

Post by dvgrn » June 17th, 2021, 9:07 am

hotdogPi wrote:
June 17th, 2021, 8:17 am
Other rules have quadratic replicators that replicate fast enough that copies just go around whatever is in their way. Is that any more likely?
Definitely maybe not, I'd say, but I don't know what I'm talking about... and I don't think anyone else does either, as far as a "more likely" judgment goes.

The only thing we know about non-engineered quadratic replicators in Life is that no small fast natural ones have showed up in any Catagolue soups yet. So if they're out there, they're not terribly likely. But we have no idea how unlikely they are.

The smallest quadratic replicator in Life fits inside some NxN bounding box. We don't know if N is 10 or 100 or 1000 or 10,000. It won't be much bigger than 10,000, for sure, since even the 0E0P metacell is only 260,000^2-ish, and that thing is programmable and way more complicated than it needs to be, in various ways.

I'm not sure how fast a metacell we could engineer, but presumably we could get close to c/4 diagonally or c/2 orthogonally the same way the Speed Demonoid and hypothetical Speed Orthogonoid can. But the fast engineered replicators mostly won't be small, and the small engineered replicators mostly won't be fast.

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Re: Structures resistant to attack

Post by yujh » June 17th, 2021, 9:20 am

hotdogPi wrote:
June 17th, 2021, 8:17 am
Other rules have quadratic replicators that replicate fast enough that copies just go around whatever is in their way. Is that any more likely?
No, for this question, you can still delete it.
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Re: Structures resistant to attack

Post by NickGotts » July 18th, 2021, 11:22 am

Just a couple of comments.
1) IRL, living things are not "resistant to attack" in the sense used in the first comment on this thread - they do resist attack, but none exist that can repel all possible attacks. And they don't reproduce in empty space; rather they require the presence of highly-structured living or nonliving elements of the environment in order to grow and reproduce.
2) I've spent a lot of time (over several decades) on "Sparse Life", where the starting point is an infinite (or arbitrarily large) very-low-density random field (I've had to suspend this work/pastime for the past year, as I've gone back into full-time employment, but that will end by the end of 2021, when i'll resume). I think it probable that quasi-living patterns will emerge and flourish in an environment consisting largely of a network of non-living linear structures. At any rate, the dynamics will be quite different from those you would find in a random field of high density, where I agree with dvgrn.

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